The Senate health-care bill would raise effective marginal tax rates on lower and middle-income singles and families up to 41%.

The effective marginal tax rate is the answer to the question: "If I earn $1 more, how much less than $1 do I get to save or spend?" If you can keep that full dollar for your disposal, the effective marginal tax rate is zero. If earning another dollar does not raise your disposable income by even a penny, the effective marginal tax rate is 100 percent.

Consider, then, the figure below constructed for a two-earner family with two school-age children, one of whom is in college. The solid line shows the EMTR based on income tax law prior to the health-care bill (it excludes the impact of the payroll taxes). The dashed line displays the damaging increases in the EMTR assuming the health insurance premium subsidies contained in the Senate health-care bill and insurance cost estimates provided by the Kaiser Family Foundation. As a family's income rises above 133% of poverty, Medicaid eligibility will be eliminated but a family that does not receive health insurance from their employer will receive a subsidy to purchase health insurance in the "exchange." In turn, however, as their efforts yield higher income, subsidies are clawed back or effectively taxed away.

How can a family be expected to get ahead when taking an extra shift, finding a way for a second parent to work, or investing in night school courses to qualify for a raise means handing the government as much as 41% of the additional income earned?

Taxes interfere with the basic rewards for work, thrift, and saving. Excessive EMTRs damage these incentives, discourage the taxed, and threaten to rob America of a vitality that is its signature.